A number of experiments were performed in order to arrive at a combination of additives for the maintenance of cytochrome P-450 in liver cells in culture at original level. A combination of 50 MuM Delta-aminolevulinic acid (ALA), 5 MuM hydrocortisone, 1 MuM dexamethasone, and 10% Nu Serum in Williams E medium proved to be the most satisfactory in maintaining cytochrome P-450 isozymes at 80-90% of original levels. Even though dexamethasone and hydrocortisone induced other proteins as shown by electrophoresis, the P-450 isozyme pattern of liver appears to be maintained as in the original cells. This is true with control as well as phenobarbital induced cytochrome P-450. [35]S-methionine was incorporated into a number of proteins in the cells. At present we are purifying the different forms by DEAE chromatography and SDS gel electrophoresis after precipitation with specific antibodies to cytochrome P-450. We have raised several monoclonal antibodies against these isozymes and these will be utilized for purification of [35]S-labeled cytochrome P-450's in cells both in the control as well as induced state. The monoclonal antibodies against cytochrome P-450 are being characterized.